Code Manual for CONTAIN 2.0 - Federation of American Scientists

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For any sectional coefficient ~, the interpolated sectional coefficients are given by
g = (1 - FT)[(l -FP)~ll + FP512 ] + %[(1 -FP)321 + FP522] (7-5)
where I& is the aerosol coefilcient for some process for the lowest atmospheric temperature (Tti~)
and pressure (P~i~),~12 is the aerosol coefficient for that process for the 10west atrnosPheric
temperature (T~i~)and highest pressure (p~m), (~21) is tie aerosol for the ~ghest atmospheric
temperature (T~m) and lowest pressure (pW,), ~d ~zz is the aerosol coefficient for the ~ghest
atmospheric temperature (T~M)and pressure (P~u).
F~ and FPin Equation (7-5) are defined as
and
Fp =
[)
Pg - Ptin
P “ Pfin
max
where T~is the atmosphere temperature, and P~is the atmosphere pressure.
It should be noted that not all aerosol modeling is cast in coefficient form, because of the limitations
discussed above. In particular, coefficients are not used for the aerosol deposition models for
engineered systems, which are discussed in Sections 7.4 through 7.6, or for the moving grid
condensation model. With regard to engineered systems, the full expressions for the deposition rates
are always used and properly evaluated with respect to local boundag layer conditions. The
deposition rate, however, is evaluated only for one representative particle diameter within each
section, taken to be the geometric mean of the upper and lower diameters in the section. This
approach is believed to be adequate. With regard to the moving grid model, the effects of
condensation or evaporation are evaluated by calculating the change in particle size with time, then
redistributing the time-evolved distribution into the fixed sections. The effects cannot be represented
in terms of the time-independent ~ coel%cients shown in Equation (7-3).
In the following discussion, for simplicity, only the discrete forms of the agglomeration kernels and
deposition rate equations will be presented. The approximations inherent in the use of the coefficient
approach, if applicable, will be indicated.
7.2.1 Agglomeration
When two aerosol particles collide, they can combine to form a larger particle. This process is
known as agglomeration or coagulation. A basic assumption about these processes is that only two
Rev O 711 6/30/97